1. Field of Invention
Metal printing plates used in fine arts such as etching and engraving must often be cut to contours which include combinations of straight lines and arcs of circles. The plates are usually of sheet zinc or copper about 1.5 mm thick. In prior practice the plates are usually cut to shape with a sheet metal shear and a bandsaw. In unpracticed hands such machines are somewhat hazardous and have been found to create difficulties with insurance in art schools; they are also heavy and bulky.
There is hence a need for a safer and more portable apparatus to cut the plates to shape. A small-diameter router bit will safely make a non-distorting cut through a printing plate in a few passes, but requires a safe and versatile guiding system.
2. Prior Art
The following U.S. Pat. Nos. are the closest prior art of which I am aware:
(a) Chapman 881,899 shows a glass cutter on a telescoping arm rotatable about a central mount held to the work with a suction disc.
(b) Pederson et al 2,943,655 shows a router guide for cutting grooves in wood parallel to other grooves, or in arcs about a recess in the work.
(c) Cherry et al 3,858,630 shows a woodworking machine with a router and a templet tracer at opposite ends of a pair of rods slidable through a pivoted central support.
(d) Killian 2,589,554 shows a guide for a portable power circular saw, which slides along two parallel rods.
(e) Balcombe 4,031,931 shows a mortising machine in which a router slides along parallel rods.
(f) Lowry et al 3,421,411 shows a follower arm to limit the depth of cut, in a weld-trimming device.
Of the above references, (a)-(c) were found in a preliminary search, and (a), (d), (e), and (f) were applied by the Examiner to claims in the prior application referred to above.